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Balance Redox Rxns: Fe(OH) 3 + [Cr(OH) 4 ] -1 Fe(OH) 2 + CrO 4 -2 in base

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Electrochemistry

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Metallic Conduction The flow of electrons through a metal

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Ionic Conduction The movement of ions (electrolytes) through a solution Electrolytic Conduct.

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Electrode The surface or point in which oxidation or reduction takes place

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Anode The electrode where oxidation takes place An Ox (-)

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Cathode The electrode where reduction takes place Red Cat (+)

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Voltaic or Galvanic Cell Electrochemical Cell in which:

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a spontaneous oxidation-reduction reaction produces electrical energy

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Half-Cell A cell where only oxidation or only reduction takes place

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An electrochemical cell must have two half-cells connected by a salt bridge

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A half-cell will not work by itself Both half-cells are required

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Salt Bridge 1) Allows electrical contact between the two half-cells

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2) Prevents mixing of the two half- cell solutions

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3) Allows ions to flow maintaining electrical neutrality

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Determining the Redox Rxn & Voltage of an Electrochemical Cell

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Identify all molecules & ions (reactants) that exist in the electrolytic cell

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1) Determine all possible half- reactions that could occur in the system

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2 ) Look up each half-rxn from the Std. Redox Tables

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3) Record each half-rxn & its standard voltage

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4) Save the oxidation half- rxn that has the highest voltage

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5) Save the reduction half- rxn that has the highest voltage

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6) Balance the electrons between the two half-rxns

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7) Add the two half-rxns to obtain the full electrochemical reaction

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7) Add the voltage of each half-rxn to obtain the std. voltage required

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Voltaic Cell Problems

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Determine all when a cell with a Cu electrode in CuCl 2(aq) is connected to a cell with a Zn electrode in ZnBr 2(aq)

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Determine all when a cell with a Fe electrode in FeCl 3(aq) is connected to a cell with a Mn electrode in MnCl 2(aq)

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Determine all when a cell with a Mg electrode in Mg(NO 3 ) 2(aq) is connected to a cell with a Au electrode in Au(NO 3 ) 3 (aq)

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Electrolysis Using electricity to force a non- spontaneous electrochemical rxn

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Electrolytic Cell Chemical cell where electrolysis is being performed

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How to determine the Redox Rxn & voltage of an Electrolytic Cell

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Identify all molecules & ions (reactants) that exist in the electrolytic cell

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1) Determine all possible half- reactions that could occur in the system

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2 ) Look up each half-rxn from the Std. Redox Tables

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3) Record each half-rxn & its standard voltage

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4) Save the oxidation half- rxn that has the highest voltage

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5) Save the reduction half- rxn that has the highest voltage

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6) Balance the electrons between the two half-rxns

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7) Add the two half-rxns to obtain the full electrochemical reaction

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7) Add the voltage of each half-rxn to obtain the std. voltage required

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Determine the rxn that takes place when 1.5 V is passed through two Pt electrodes in a solution containing MgI 2(aq) & ZnCl 2(aq)

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Determine the rxn that takes place when 2.5 V is passed through two Pt electrode in a solution of NaCl (aq) 0

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Determine the rxn that takes place when 2.0 V& 9.65 A is passed for 2.5 Hrs through two Pt electrodes in a solution containing MnBr 2(aq) & AlF 3(aq)

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Relating Equations G o = H o - T S o G o = -RTlnK eq G o = -nF E o

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Nernst Equation E = E o - (RT/nF)lnQ for non-standard conditions

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Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & an iron electrode in 0.10 M Fe(NO 3 ) 2 at 27 o C

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Determine the voltage of a cell with a silver electrode in 1.0 M AgNO 3 & a zinc electrode in 0.010 M Zn(NO 3 ) 2 at 27 o C

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Determine the voltage of a cell with a copper electrode in 0.10 M CuNO 3 & a zinc electrode in 1.0 M Zn(NO 3 ) 2 at 27 o C

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Electroplating & Electro-purifying

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Electrolysis During electrolysis, oxidation & degradation would occur at the anode while reduction & electroplating would occur at the cathode

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Current Formula Current = charge/unit time Amps = coul/sec Amount (mass, volume, moles, etc) can be determined from the charge

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Calculate the mass of copper plated onto the cathode when a 9.65 mAmp current is applied to a solution of CuSO 4 for 5.0 minutes.

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Calculate the years required to plate 216 kg onto the cathode when a 96.5 mAmp current is applied to a solution of AgNO 3

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Calculate the current required to purify 510 kg of aluminum oxide in 5.0 hours

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Calculate the time required to electroplate 19.7 mg of gold onto a plate by passing 965 mA current through a solution of Au(NO 3 ) 3

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Calculate the time required to gold plate a 2.0 mm layer onto a 250 cm 2 by passing 965 mA current through a solution of Au(NO 3 ) 3 (D Au = 20 g/cm 3 )

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Calculate the time required to purify a 204 kg of ore that is 60.0 % Al 2 O 3 by applying a 965 kA current through molten ore sample:

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Calculate the time required to purify a 32 kg of ore that is 75.0 % Fe 2 O 3 by applying a 9.65 kA current through molten ore sample:

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Determine the voltage of a cell with a silver electrode in 5.0 M AgNO 3 & an zinc electrode in 0.25 M Zn(NO 3 ) 2 at 27 o C

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